Winters in Santo Tirso are cool and unpredictable, with temperatures often fluctuating between freezing and mild conditions. Temperatures typically range from -5°C to 15°C in January, averaging around 8°C. As spring approaches, temperatures gradually rise, reaching averages of 14°C by April and May. Summer brings warmer and more stable weather, with July and August experiencing average highs of 19°C, although occasional heatwaves can push temperatures above 36°C. Autumn sees a return to milder conditions, with November and December averaging around 11-12°C.